I. Field of the Invention
This invention relates generally to implantable, programmable, cardiac stimulating apparatus, and more particularly to a method for determining and manually or automatically programming the device so that it operates in a stimulating mode and with stimulating cycle parameters that optimize one or more cardiac performance parameters of the patient, such as, cardiac output, mean arterial pressure, pO.sub.2 or pCO.sub.2, etc.
II. Discussion of the Prior Art
A paper entitled "Usefulness of Physiologic Dual-Chamber Pacing in Drug-Resistant Idiopathic Dilated Cardiomyopathy" by Margarete Hochleitner, et al. (Am J Cardiol 1990; 66:198-202), describes the beneficial effects of dual-chamber (DDD) pacing on critically ill patients suffering from chronic heart failure. The patients involved in the underlying study were treated by implanting a DDD cardiac pacemaker whose atrial electrode was positioned near the right auricle and the ventricular electrode was positioned in the apical region of the right ventricle. The implanted pacemaker was programmed to have an atrioventricular (AV) interval of 100 ms when pacing in the DDD mode. The 100 ms AV interval was chosen as that offering the shortest possible delay that did not significantly impair cardiac function. The cardiac function was evaluated through echocardiographic studies and then the pacemaker was manually programmed to function with an AV delay of 100 ms as a compromise between a shorter value that resulted in poor right ventricular compliance and a larger value that failed to show any significant improvement in cardiac function. The Hochleitner paper describes in detail the marked improvement in cardiac performance of the CHF patients due to the DDD pacing at the 100 ms AV delay interval.
As is explained in a copending application of Julio C. Spinelli et al. Serial No. 07/339,815, filed Nov. 14, 1994, and entitled "Method and Apparatus to Continuously Optimize AV Delay in a Dual Chamber Pacemaker", patients exhibiting CHF typically have a very narrow range for the optimum AV delay, meaning that small deviations, e.g., only 10 ms, from the optimum can diminish the clinical benefit obtained using DDD pacing. Thus, arbitrarily setting the AV delay at a fixed programmed value, based upon echocardiographic data as set out in the Hochleitner paper, may not guarantee the optimum benefit obtainable to CHF patients using DDD pacing. It would, therefore, be advantageous to have a system that would automatically and periodically determine whether both the pacing mode and a controlled pacing cycle parameter are optimal for a given patient and, if not, they automatically, or with cardiologist intervention, effect a reprogramming of an implanted DDD pacemaker so that it is made to operate in a pacing mode and with a cardiac cycle parameter that results in an optimum benefit to the patient in terms of a measured cardiac performance parameter. Thus, for example, if the cardiac performance parameter of interest is cardiac output, it would be advantageous to have a programmable implantable DDD pacemaker whose AV delay and whose pacing mode results in a maximum cardiac output.
Accordingly, it is a principal object of the present invention to provide a cardiac stimulation device capable of dual chamber pacing and capable of operating in any one of a plurality of modes with the necessary implantable or external sensing/monitoring structure for iteratively altering a cardiac cycle pacing parameter, such as AV interval, between an initial value and a predetermined maximum value and for determining for each successive iterative change the associated value of the cardiac performance parameter being measured so that when all possible pacing modes and pacing cycle parameters have been utilized, a determination can be made as to which pacing mode and which cardiac cycle parameter achieved the optimum cardiac performance. Once that pacing mode and pacing cycle parameter is determined, the implanted cardiac stimulation device can be programmed to function in that mode and with that cycle pacing parameter.